The common approach for installing dock levellers in pits of loading dock installations is to weld, or in some other manner permanently secure the dock leveller in the pit. U.S. Pat. No. 3,316,575 to Larsen et al discloses a type of mechanical dock leveller. The dock leveller includes a frame to which a ramp is hinged for swinging movement. Extension springs in combination with a lever arm are used to raise the dock for purposes of lowering it onto a truck bed to bridge the gap between the dock installation and the level of a truck bed.
Mechanical dock levellers are only one type. Another type is that commonly referred to as a hydraulic dock leveller. A typical unit is disclosed in Canadian Pat. No. 935,606 to Larsen et al. The hydraulic dock leveller also comprises a frame to which a ramp is hinged. Instead of extension springs and mechanical linkage, the ramp is raised and lowered by use of a controlled hydraulic cylinder arrangement. In each instance, the frame portion to which the ramp is hinged is secured in the pit by welding the frame to steel components, which may be embedded in the concrete. Commonly, the rear portion of the frame is welded to a steel beam which is embedded in the end wall of the concrete pit. The forward portion of the leveller frame is welded to steel components which are also embedded in the pit concrete bottom. In some installations where the steel components have not been embedded in the concrete, they are set in the concrete by the use of lag bolts or the like. Lag bolts tend to corrode and eventually become permanently fixed in the concrete due to the corrosion and thus are not readily removable from the concrete.
Other forms of mechanical dock levellers are disclosed in Kumpolt, Canadian Pat. No. 766,440 and in U.S. Pat. No. 3,137,876 to Loomis Machine Co. In both of these patents, the dock levellers are permanently secured in the concrete of the dock loading installation.
Kelley Company Inc. discloses in its U.S. Pat. No. 4,014,059 an arrangement having levelling feet which are welded in position as they engage the pit bottom. Once the dock is levelled, it is welded to a plate embedded in the concrete at the rear of the pit to permanently secure the dock leveller.
Ambli discloses in U.S. Pat. No. 3,122,764 a mini-dock leveller which is bolted to the loading dock installation. This suffers the same problems as with the use of lag bolts. They corrode and usually require the use of a torch or the like to cut the bolts so that the dock platform can be removed for service, replacement or cleaning.
To provide for flexibility in the use of a dock leveller, Kumpolt, U.S. Pat. No. 3,639,935, discloses a portable dock leveller which is mounted on wheels and may be transported from area to area for use in bridging different heights. A similar approach in providing for a portable platform is disclosed by Miles in U.S. Pat. No. 3,261,489. The unit may be readily picked up by the use of a fork lift truck and put in position to provide for traffic movement from one level to another.
As to the aspect of providing for removability of platforms and ramps, couplers are disclosed in U.S. Pat Nos. 3,296,639 and 3,735,440. These coupling arrangements are particularly adapted for use with ship installations.
The dock leveller, as embodied in this invention, provides for releasably securing the dock leveller to the dock to permit ready removal of the dock leveller for repair, replacement and/or cleaning.